1. Field
Example embodiments generally relate to a jet pump inspection apparatus including an encoded probe driver coupled to a hybrid form guide funnel that introduces probe cable assemblies to boiling water reactor (BWR) jet pump assemblies.
2. Description of Related Art
Bores such as pipes or cylindrically shaped equipment are often submerged in a pool of water or other liquid. There is often a need to have a maintenance tool or inspection probe delivered into the submerged bore. For example, a reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has submerged bores that need to be inspected during maintenance routines. Hollow tubular jet pumps having internal bores are positioned within an annulus to provide the required reactor core water flow. The jet pump includes an upper portion, known as the inlet mixer, and a lower portion, known as the diffuser. The inlet mixer and the diffuser, due to their large size, are formed by welding a plurality of cylindrical and conical sections together. Specifically, respective ends of adjacent cylindrical sections are joined with a circumferential weld. During operation of the reactor, the circumferential weld joints may experience inter-granular stress corrosion cracking (IGSCC) and irradiation assisted stress corrosion cracking (IASCC) in weld heat affected zones. This can diminish the structural integrity of the jet pump.
It is important to examine the welds of the jet pump inlet mixer and diffuser periodically to determine whether any cracking has occurred. While visual examinations in the annulus or region between a shroud and a pressure vessel wall can be performed, these examinations are likely to be only partial inspections due to access limitations in the annular region of the reactor. As such, the examination of the jet pump welds are often examined by an inspection tool positioned inside of the jet pump inlet mixer and jet pump diffuser. Such inspection tools perform ultrasonic and/or eddy current examinations of jet pump welds from inside the jet pump inlet mixer and diffuser in a nuclear reactor.
Typically, operational personnel located on a 360° service platform above the surface of the pool manipulate poles and other mechanical suspension devices to position a funnel to the inlet mixer of each jet pump to be inspected. In some cases the tool is deployed from a refuel bridge or auxiliary bridge. For a single BWR, there are typically 20 jet pumps, but a BWR can have up to 24. Prior to installing the delivery tool into the pool, the probe head with cable is loaded into the delivery tool. Once the delivery tool is positioned at the inlet of a jet pump inlet, the funnel is secured to the inlet using a pneumatic clamp. As the inlets to the jet pumps are submerged, often up to 50 feet under the surface of the pool, the manual manipulation of these poles and the funnel is difficult and time consuming.
After the tool delivery system is mated with the inlet mixer, the inspection tool or probe is lowered into a calibrated reference sleeve to calibrate the ultrasonic probes prior to inspection. The scan head is then lowered into the inlet of the pump to commence with the inspection. Once the first adjacent jet pump is inspected, the scan head is positioned into the calibration sleeve and post inspection calibration is performed. The tool delivery system is then disconnected and moved to the next pump. The attachment, calibration, insertion, and inspection operations are repeated until all jet pumps have been inspected. Often the operator will utilize at least one submerged camera to aid in the movement, manipulation, attachment, and detachment of the submerged components.
The probe driver is located as close as possible to the inlet of the pump to reduce the position error resulting from cable stretch between the positioning device and the scan head. In other systems and methods, a probe driver assembly can be located above the pool surface. Such a probe driver assembly provides for axial movement of the inserted probe by using a take-up reel and a set of pinch wheels to raise and lower the probe head. However, such systems have often been considered difficult to maintain accurate position.
As such, current systems and methods for inspecting the inside of a submerged bore such as a nuclear reactor jet pump that can be submerged 50 feet below the surface of a water pool are difficult, time consuming, and costly. Often such tasks become a critical path item during a nuclear reactor reloading process. As such, any opportunity for reducing the required time can decrease the amount of off-line or down-time of the reactor and therefore provide significant cost savings to the reactor operator as well as reduced dose to operators and technicians.